Process and apparatus for treating a workpiece with steam and ozone

ABSTRACT

In a method for processing a workpiece to remove material from a first surface of the workpiece, steam is introduced onto the first surface under conditions so that at least some of the steam condenses and forms a liquid boundary layer on the first surface. The condensing steam helps to maintain the first surface of the workpiece at an elevated temperature. Ozone is provided around the workpiece under conditions where the ozone diffuses through the boundary layer and reacts with the material on the first surface. The temperature of the first surface is controlled to maintain condensation of the steam.

[0001] This Application is a Continuation of U.S. patent applicationSer. No. 09/621,028, filed Jul. 21, 2000 and now pending, which is aContinuation-in-Part of International Patent Application PCT/US99/08516,filed Apr. 16, 1999, and now expired, which is a Continuation-in-Part ofU.S. patent application Ser. No. 09/061,318, filed Apr. 16, 1998, andnow abandoned, which is a Continuation-in-Part of U.S. patentapplication Ser. No. 08/853,649, filed May 7, 1997, and now U.S. Pat.No. 6,240,933. Priority to these Applications is claimed under 35 U.S.C.§§119 and 120. U.S. patent application Ser. No. 09/621,028 isincorporated herein by reference.

[0002] The cleaning of semiconductor wafers is often a critical step inthe fabrication processes used to manufacture integrated circuits or thelike. The geometries on wafers are often on the order of fractions of amicron, while the film thicknesses may be on the order of 20 Angstroms.This renders the devices highly susceptible to performance degradationdue to organic, particulates or metallic/ionic contamination. Evensilicon dioxide, which is used in the fabrication structure, can beconsidered a contaminant if the quality or thickness of the oxide doesnot meet design parameters.

[0003] Although wafer cleaning has a long history, the era of “modern”cleaning techniques is generally considered to have begun in the early1970s when RCA developed a cleaning sequence to address the varioustypes of contamination. Although others developed the same or similarprocesses in the same time frame, the general cleaning sequence in itsfinal form is basically the same.

[0004] The first step of the RCA cleaning sequence involves removal oforganic contamination using sulfuric acid and hydrogen peroxidemixtures. Ratios are typically in the range of 2:1 to 20:1, withtemperatures in the range of 90-140 degrees Celsius. This mixture iscommonly called “piranha.” A recent enhancement to the removal oforganic contamination replaces the hydrogen peroxide with ozone that isbubbled or injected into the sulfuric acid line.

[0005] The second step of the process involves removal of oxide filmswith water and HF (49%) in ratios of 200:1 to 10:1, usually at ambienttemperatures. This processing typically leaves regions of the wafer in ahydrophobic condition.

[0006] The next step of the process involves the removal of particlesand the re-oxidation of hydrophobic silicon surfaces using a mixture ofwater, hydrogen peroxide, and ammonium hydroxide, usually at atemperature of about 60-70 degrees Celsius. Historically, ratios ofthese components have been on the order of 5:1:1. In recent years, thatratio has more commonly become 5:1:0.25, or even more dilute. Thismixture is commonly called “SC1” (standard clean 1) or RCA1.Alternatively, it is also known as HUANG1. Although this portion of theprocess does an outstanding job of removing particles by simultaneouslygrowing and etching away a silicon dioxide film on the surface of a baresilicon wafer (in conjunction with creating a zeta potential whichfavors particle removal), it has the drawback of causing metals, such asiron and aluminum, in solution to deposit on the silicon surface.

[0007] In the last portion of the process, metals are removed with amixture of water, hydrogen peroxide, and hydrochloric acid. The removalis usually accomplished at around 60-70 degrees Celsius. Historically,ratios have been on the order of 5:1:1, but recent developments haveshown that more dilute chemistries are also effective, including dilutemixtures of water and HCl. This mixture is commonly referred to as “SC2”(standard clean 2), RCA2, or HUANG2.

[0008] The foregoing steps are often run in sequence, constituting whatis called a “pre-diffusion clean.” Such a pre-diffusion clean insuresthat wafers are in a highly clean state prior to thermal operationswhich might incorporate impurities into the device layer or cause themto diffuse in such a manner as to render the device useless. Althoughthis four-step cleaning process is considered to be the standardcleaning process in the semiconductor industry, there are manyvariations of the process that use the same sub-components. For example,the piranha solution may be dropped from the process, resulting in aprocessing sequence of: HF->SC1->SC2. In recent years, thin oxides havebeen cause for concern in device performance, so “hydrochloric acidlast” chemistries have been developed. In such instances, one or more ofthe above-noted cleaning steps are employed with the final cleanincluding hydrochloric acid in order to remove the silicon backside fromthe wafer surface.

[0009] The manner in which a specific chemistry is applied to the waferscan be as important as the actual chemistry employed. For example, HFimmersion processes on bare silicon wafers can be configured to beparticle neutral. HF spraying on bare silicon wafers typically showsparticle additions of a few hundred or more for particles at 0.2 micronsnominal diameter.

[0010] Although the four-chemistry clean process described above hasbeen effective for a number of years, it nevertheless has certaindeficiencies. Such deficiencies include the high cost of chemicals, thelengthy process time required to get wafers through the various cleaningsteps, high consumption of water due to the need for extensive rinsingbetween chemical steps, and high disposal costs. The result has been aneffort to devise alternative cleaning processes that yield results asgood as or better than the existing four-chemistry clean process, butwhich are more economically attractive.

[0011] Various chemical processes have been developed in an attempt toreplace the existing four-chemistry process. However, such cleaningprocesses have failed to fully address all of the major cleaningconcerns of the semiconductor processing industry. More particularly,they have failed to fully address the problem of minimizingcontamination from one or more of the following contaminants: organics,particles, metals/ions, and silicon dioxide.

[0012] Accordingly, there is a need for improved systems and methods forprocessing and cleaning wafers or workpieces

SUMMARY OF THE INVENTION

[0013] In a first aspect, in a method for processing a workpiece toremove material from a first surface of the workpiece, steam isintroduced onto the first surface under conditions so that at least someof the steam condenses and forms a liquid boundary layer on the firstsurface. The condensing steam helps to maintain the first surface of theworkpiece at an elevated temperature. Ozone is provided around theworkpiece under conditions where the ozone diffuses through the boundarylayer and reacts with the material on the first surface. The temperatureof the first surface is controlled to maintain condensation of thesteam.

[0014] In a second aspect, the temperature of the first surface iscontrolled via a heat sink in contact with the workpiece.

[0015] In a third aspect, the temperature of the first surface iscontrolled via a temperature-controlled stream of liquid delivered tothe second or back surface of the workpiece, while steam and ozone aredelivered to an enclosed process region and the steam condenses on thefirst or front surface.

[0016] In a fourth aspect, the workpiece is rotated while the steamcondenses.

[0017] In a fifth aspect, additives, such as hydrofluoric acid, ammoniumhydroxide or other chemicals may be added to promote cleaning.

[0018] The methods of the invention allow for use of high temperatureswhich are advantageous is speeding up the reaction times for removingorganic or other materials from the surface of the workpiece. Themethods of the invention also have the potential for removing ofdifficult to remove materials, which may require more energy for removalthan can be readily provided using only hot water.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a schematic block diagram of one embodiment of anapparatus for treating a semiconductor workpiece in which ozone isinjected into a line containing a pressurized treatment liquid.

[0020]FIG. 2 is a schematic block diagram of one embodiment of anapparatus for treating a semiconductor workpiece in which thesemiconductor workpiece is indirectly heated by heating a treatmentliquid that is sprayed on the surface of the workpiece.

[0021]FIG. 3 is a flow diagram illustrating one embodiment of a processflow for treating a semiconductor workpiece with a treatment fluid andozone.

[0022]FIG. 4 is a schematic block diagram of an alternative embodimentof the system set forth in FIG. 2 wherein the ozone and treatment fluidare provided to the semiconductor workpiece along different flow paths.

[0023]FIG. 5 is a schematic block diagram of an embodiment of anapparatus for treating a semiconductor workpiece in which pressurizedsteam and ozone are provided in a pressurized chamber containing asemiconductor workpiece.

[0024]FIG. 6 is a schematic block diagram of an embodiment of anapparatus for treating a semiconductor workpiece in which anultra-violet lamp is used to enhance the kinetic reactions at thesurface of the workpiece.

[0025]FIG. 7 is a schematic block diagram of an embodiment of anapparatus for treating a semiconductor workpiece in which liquid gascontactors are used to enhance the kinetic reactions at the surface ofthe workpiece.

DETAILED DESCRIPTION OF THE INVENTION

[0026] A novel chemistry, application technique, and system is used toreduce the contamination and speed up processing in the manufacturing ofsemiconductor wafers, memory disks, photomasks, optical media, and othersubstrates (collectively referred to here as “wafers”) requiring a highlevel of clean. Contamination may occur from organics, particles,metal/ions, and silicon dioxide. Cleaning of wafers is achieved bydelivery of a chemical stream to the workpiece surface. Ozone isdelivered either into the liquid process stream or into the processenvironment. The chemical stream, which may be in the form of a liquidor vapor, is applied to the wafer in a system which allows for controlof the liquid boundary layer thickness. The chemical stream may includeammonium hydroxide for simultaneous particle and organic removal,another chemical to raise the pH of the solution, or other chemicaladditives designed to accomplish one or more specific cleaning steps.

[0027] Wafers are preferably placed in a standard Teflon wafer cassette,or in a centrifugal process chamber utilizing a “carrierless” rotordesign. During processing, the wafers and/or cassette are preferablyrotated in the chamber.

[0028] A processing solution is preferably heated and sprayed onto thewafer surface. This heats the surface of the wafer as well as theenvironment. If the spray is shut off, a thin liquid film remains on thewafer surfaces. However, preferably the liquid spray is continued forthe duration of the chemical process step. If the wafer surface ishydrophobic, a surfactant may be added to the liquid chemical to createa thin film of liquid on the surfaces. The boundary layer of theprocessing solution at the wafer surface is advantageously controlledthrough the use of the rotation rate, the flow rate of the processingsolution, and/or the injection technique (nozzle design) used to deliverthe liquid (or steam) stream to the surfaces of the wafers.

[0029] Ozone is concurrently injected into the enclosed chamber duringthe liquid spray, either through the same manifold as the liquiddelivery or through a separate manifold. Ozone injection may continueafter the spray has shut off. If the wafer surfaces begin to dry (as inthe case of a non-continuous spray), a brief spray may be used toreplenish the liquid. This insures that the exposed wafer surfacesremain wetted at all times and that the elevated temperature at thewafer surfaces is also maintained. The process may also be used on asingle wafer, rather than on an entire batch.

[0030] While ozone has a limited solubility in the hot liquid solution,it is still able to diffuse through the solution and react with thesurface of the wafer (whether it is silicon, photoresist, etc.) at theliquid/solid interface. Thus diffusion, rather than dissolution, is theprimary mechanism used to deliver ozone to the surfaces of the wafers.Water apparently helps to hydrolyze carbon-carbon bonds or acceleratethe oxidation of silicon surfaces by hydrolyzing silicon-hydrogen orsilicon-hydroxyl bonds. The elevated temperature promotes the reactionkinetics and the high concentration of ozone in the gas phase promotesdiffusion of the ozone through the liquid film, even though theincreased temperature of the liquid film does not result in a solutionhaving a high concentration of ozone dissolved in it.

[0031] The flow of ozone can be delivered to the process chamber througha vapor generator or the like. Such a generator is filled with water,which is temperature controlled. Thus the ozone gas stream is enrichedwith water vapor which maintains the boundary layer on each wafersurface at a minimal thickness so that the layer does not inhibitdiffusion. At the same time, such delivery assists in preventing thewafers from drying completely during the process.

[0032] A high capacity ozone generator is preferably used to produce amixed effluent containing a high concentration of ozone in combinationwith a high flow rate. A higher concentration of ozone increases thequantity of ozone provided to the surface of the wafer. A higher flowrate increases the rate at which fresh reactants are replenished, andspent or exhausted reactants are carried away from the wafer.

[0033] Purely maximizing the concentration of ozone is not optimal forprocess performance, as the amount of ozone then generated is then toosmall to create an adequate concentration within the process chamber. Onthe other hand, simply maximizing flow rate or volume, withoutsufficient concentration will result in rapid depletion of ozone in theprocess chamber ( as the ozone will react rapidly with organic materialsin the process chamber ). Thus, both high concentration and high flowrates are needed.

[0034] In known spray processing operations, wafer rotational speeds arein the range of 10-100 rpm. Such low speeds tend to allow a thickboundary layer of liquid to build up on the surfaces of the wafers tocreate a diffusion barrier, which, in turn, inhibits the reaction rate.It has been found, however, that a continuous spray of liquid, such asthe de-ionized water that is heated to maintain the surface temperatureof the wafers, combined with high rotational speeds (>300 rpm),generates a very thin boundary layer that minimizes the diffusion layerthickness thereby leading to an enhanced stripping rate. It has alsobeen found that increases in the rotational rate of the wafers duringprocessing results in a corresponding increase in the strip rate. Forexample, an increase in the rotational rate from 300 to 800 rpm resultsin the strip rate increasing by a factor of 2 or more. A furtherincrease to 1500 rpm has been seen to result in another two-foldincrease. Rotation rates of up to 3000 rpm are anticipated.

[0035] To further enhance the process, the temperature of the liquidsupply (water supply) can be heated to generate a supply of saturatedsteam under pressure to the process chamber. Under such circumstances,it is possible to achieve wafer surface temperatures in excess of 100degrees Celsius, thereby further accelerating the reaction kinetics. Asteam generator may be used to pressurize the process chamber to achievethe desired temperatures. For example, saturated steam at 126 degreesCelsius may be used with a corresponding increase in the pressure of theprocess chamber to 240 K Pa (35 psia). The increased pressure within theprocessing chamber also provides for use of higher ozone concentrations,thereby generating a higher diffusion gradient across the boundary layerat the surface of each wafer. Still further, the use of steam alsoallows for the use of lower rotation rates to achieve the requisite thinboundary layers at the surfaces of the wafers. The oxidation rate of theozone may also be enhanced by irradiating the surfaces of the waferswith ultra-violet light.

[0036] The invention allows particles, metals, and organics to beremoved in a single processing step. Further, it is now possible toregenerate a fresh, clean, controlled chemical oxide film in that samestep. To this end, certain additives may be provided in the processingliquid to specifically target certain contaminants and/or to enhance theeffectiveness of the overall process. For example, ammonium hydroxidemay be added to the processing liquid (e.g., deionized water) to reduceparticle counts on the workpieces. In such a process, the ozone preventspitting of the silicon surface by the ammonium hydroxide.

[0037] Other additives that enhance the cleaning capability of theoverall process include HF and HCl. Such additives have the followingbenefits/effects: 1) removal of organic contaminants; 2) removal ofoxide and regeneration of a controlled chemical oxide; 3) removal ofparticles; 4) removal of metals.

[0038] After one or more of the foregoing cleaning process steps hasbeen completed, the wafers are prepared for subsequent cleaning steps.The wafers are preferably rinsed with deionized water or a suitableaqueous solution. At this time, the ozone within the processing chambermay also be purged with, for example, a nitrogen flush.

[0039] If an additive that enhances the metal removal capabilities ofthe solution is not used, it may be desirable to execute a furtherprocessing step for metal removal. In one or more such cleaning steps,metal and/or silicon dioxide may be removed from the surfaces of thewafers by applying a temperature controlled mixture containinghydrofluoric acid and/or hydrochloric acid, chloroacetic acid, or otherhalogenated chemistry. Ozone may or may not be introduced into theliquid stream or the process environment during this step.

[0040] After one or more of the foregoing steps have been completed,including any intermediate cleaning steps, the wafers are subject to afinal rinsing in deionized water or an aqueous solution. After therinse, the wafers may be dried in a manner that may include the use ofheated nitrogen, another inert gas flow, or organic vapors.Additionally, the wafers may be rotated during the drying process.

[0041] The disclosed process is applicable to various manufacturingsteps that require cleaning or selective removal of contaminants fromthe surface of a workpiece. For example, one or more of the steps may beused to remove photoresist from the surface of a semiconductor wafer. Alayer of photoresist and a corresponding layer of an anti-reflectivecoating (ARC) may be removed in a single processing step using a singleprocessing solution. An aqueous solution having a high pH, such as asolution of ammonium hydroxide and/or tetra-methyl ammonium hydroxideand deionized water, may be used to form a controlled boundary layerthat cooperate with ozone to remove both the photoresist and theanti-reflective coating.

[0042] Novel aspects include:

[0043] 1) The use of a temperature controlled liquid chemical sourcedelivered to the wafer surface to stabilize the temperature of the waferand, depending on the liquid utilized, provide a supply of water tosupport hydrolysis of the carbon-carbon bonds of contaminants at thesurface of each wafer.

[0044] 2) The control of the thickness of the boundary layer of liquidpresent on the wafer surface so that it is not of sufficient thicknessto significantly inhibit the diffusion of ozone to the wafer surface. Assuch, the ozone is allowed to diffuse through the controlled boundarylayer, where it can oxidize silicon, organics, or metals at the surface,or otherwise support any desired reaction. The boundary layer may becontrolled through the control of wafer rotation rate, vapor delivery,controlled liquid spray, the use of steam, the use of surfactants or acombination of more than one of these techniques.

[0045] 3) The process takes place in an enclosed processing chamber,which may or may not be used to produce a pressurized processingenvironment.

[0046] 4) The process utilizes a mixed effluent having a higherconcentration of ozone in combination with a higher flow rate forincreasing the rate at which fresh reactants are supplied to the surfaceof the wafer.

[0047] The invention resides as well in sub-combinations of the methodsand apparatus

[0048] Apparatus for supplying a mixture of a treatment liquid and ozonefor treatment of a surface of a workpiece, such as a semiconductorworkpiece, to execute the foregoing processes are set forth below. Thepreferred embodiment of the apparatus comprises a liquid supply linethat is used to provide fluid communication between a reservoircontaining the treatment liquid and a treatment chamber housing thesemiconductor workpiece. A heater heats the workpiece, either directlyor indirectly. Preferably, the workpiece is heated by heating thetreatment liquid that is supplied to the workpiece. One or more nozzlesaccept the treatment liquid from the liquid supply line and spray itonto the surface of the workpiece while an ozone generator providesozone into an environment containing the workpiece.

[0049] Referring to FIG. 1, the treatment system, shown generally at 10,includes a treatment chamber 15 that contains one or more workpieces 20,such as semiconductor wafer workpieces. Although the illustrated systemis directed to a batch workpiece apparatus, it is readily adaptable foruse in single workpiece processing as well.

[0050] The semiconductor workpieces 20 are preferably supported withinthe chamber 15 by one or more supports 25 extending from, for example, arotor assembly 30. Rotor assembly 30 may seal with the housing of thetreatment chamber 15 to form a sealed, closed processing environment.Further, rotor assembly 30 is provided so that the semiconductorworkpieces 20 may be spun about axis 35 during or after treatment withthe ozone and treatment liquid.

[0051] The chamber 15 has a volume which is minimized, and is as smallas permitted by design considerations for any given capacity (i.e., thenumber and size of the substrates to be treated). The chamber 15 ispreferably cylindrical for processing multiple wafers in a batch, or aflatter disk-shaped chamber may be used for single wafer processing.Typically, the chamber volume will range from about 5 liters, (for asingle wafer) to about 50 liters (for a 50 wafer system).

[0052] One or more nozzles 40 are disposed within the treatment chamber15 to direct a spray mixture of ozone and treatment liquid onto thesurfaces of the semiconductor workpieces 20 that are to be treated. Inthe illustrated embodiment, the nozzles 40 direct a spray of treatmentfluid to the underside of the semiconductor workpieces 20. However, thefluid spray may be directed alternatively, or in addition, to the uppersurface of the semiconductor workpieces 20. The fluid may also beapplied in other ways besides spraying, such as flouring, bulkdeposition, immersion, etc.

[0053] Treatment liquid and ozone are preferably supplied to the nozzles40 by system components uniquely arranged to provide a single fluid linecomprising ozone mixed with the treating liquid. A reservoir 45 definesa chamber 50 in which the liquid that is to be mixed with the ozone isstored. The chamber 50 is in fluid communication with, or connected to,the input of a pump mechanism 55. The pump mechanism 55 provides theliquid under pressure along a fluid flow path, shown generally at 60,for ultimate supply to the input of the nozzles 40. The preferredtreatment fluid is deionized water. Other treatment fluids, such asother aqueous or non-aqueous solutions, may also be used.

[0054] Fluid flow path 60 may include a filter 65 to filter outmicroscopic contaminants from the treatment fluid. The treatment fluid,still under pressure, is provided at the output of the filter 65 (ifused) along fluid flow line 70. Ozone is injected along fluid flow line70. The ozone is generated by ozone generator 75 and is supplied alongfluid flow line 80 under pressure to fluid flow line 70. Optionally, thetreatment liquid, now injected with ozone, is supplied to the input of amixer 90 that mixes the ozone and the treatment liquid. The mixer 90 maybe static or active. From the mixer 90, the treatment liquid and ozoneare provided to be input of nozzles 40 which, in turn, spray the liquidon the surface of the semiconductor workpieces 20 that are to be treatedand, further, introduce the ozone into the environment of the treatmentchamber 15.

[0055] To further concentrate the ozone in the treatment liquid, anoutput of the ozone generator 75 may be supplied to a dispersion unit 95disposed in the liquid chamber 50 of the reservoir 45. The dispersionunit 95 provides a dispersed flow of ozone through the treatment liquidto thereby add ozone to the fluid stream prior to injection of a furtheramount of ozone along the fluid path 60.

[0056] In the embodiment of the system of FIG. 1, spent liquid inchamber 15 is provided along fluid line 105 to, for example, a valvemechanism 110. The valve mechanism 110 may be operated to provide thespent liquid to either a drain output 115 or back to the liquid chamber50 of the reservoir 45. Repeated cycling of the treatment liquid throughthe system and back to the reservoir 45 assists in elevating the ozoneconcentration in the liquid through repeated ozone injection and/orozone dispersion.

[0057] The ozone generator 75 is preferably a high capacity ozonegenerator. One example of a high capacity ozone generator is the ASTeX8403 Ozone Generator, manufactured by Applied Science and Technology,Inc., Woburn, Mass., U.S.A. The ASTeX 8403 has an ozone productionrating of 160 grams per hour. At this rate a flow of approximately 12liters/minute and having a concentration of 19% ozone, by weight, can besupported. Another example of a suitable high capacity ozone generatoris the Sumitomo GR-RL Ozone Generator, manufactured by SumitomoPrecision Products Co., Ltd., Hyogo, Japan which has an ozone productionrating of 180 g/hr. The ozone generator 75 preferably has a capacity ofat least 90 or 100 grams per hour, or 110 or 120 grams per hour, withthe capacity more preferably of at least 135 grams per hour. In terms offlow rate and concentration, the capacity should be at least 10 litersper minute at 12%, 13%, 14%, 15% (or higher) concentration by weight.Lower flow rate applications, such as with single wafer processing, mayhave higher concentrations of e.g., 16-19 or greater.

[0058] Use of a high capacity ozone generator is especially useful inconnection with the methods and apparatus of the present application,because the present methods and apparatus provide for the delivery ofozone independent of the processing fluid.

[0059] In previous methods the ozone was dissolved into the aqueoussolution in order to make it available for the oxidation process on thesurface of the semiconductor wafer. This limited the amount of ozone,which could be delivered to the surface of the semiconductor wafer, tothe amount of ozone which could be dissolved into the processing fluid.Correspondingly, there was no incentive to use higher capacity ozonegenerators, because any excess ozone produced would not be absorbed bythe process fluid, and would eventually dissipate and be lost.

[0060]FIG. 1, (as well as the other Figures) illustrates variouscomponents and connections. While showing preferred designs, thedrawings include elements which may or may not be essential to theinvention. The elements essential to the invention are set forth in theclaims. The drawings show both essential and non-essential elements.

[0061] A further embodiment of a system for delivering a fluid mixturefor treating the surface of a semiconductor workpiece is illustrated inFIG. 2. Although the system 120 of FIG. 2 appears to be substantiallysimilar to the system 10 of FIG. 1, there are significant differences.The system 120 of FIG. 2 is based in part on the concept that theheating of the surfaces of the semiconductor workpieces 20 with a heatedliquid that is supplied along with a flow of ozone that creates anozonated atmosphere is highly effective in photoresist stripping, ashremoval, and/or cleaning processes. The system 120 therefore preferablyincludes one or more heaters 125 that are used to heat the treatmentliquid so that it is supplied to the surfaces of the semiconductorworkpieces at an elevated temperature that accelerates the surfacereactions. It is also possible to directly heat the workpieces tostimulate the reactions. Such heating may take place in addition to orinstead of the indirect heating of the workpieces through contact withthe heated treatment liquid. For example, supports 25 may includeheating elements that may be used to heat the workpieces 20. The chamber15 may include a heater for elevating the temperature of the chamberenvironment and workpieces.

[0062] The preferred treatment liquid is deionized water, since itappears to be required to initiate the cleaning/removal reactions at theworkpiece surface, apparently through hydrolysis of the carbon-carbonbonds of organic molecules. However, significant amounts of water canform a continuous film on the semiconductor workpiece surface. This filmacts as a diffusion barrier to the ozone, thereby inhibiting reactionrates. The boundary layer thickness is controlled by controlling the rpmof the semiconductor workpiece, vapor delivery, and controlled sprayingof the treatment liquid, or a combination of one or more of thesetechniques. By reducing the boundary layer thickness, the ozone isallowed to diffuse to the surface of the workpieces and react with theorganic materials that are to be removed.

[0063]FIG. 3 illustrates one embodiment of a process that may beimplemented in the system of FIG. 2 when the system 120 is used, forexample, to strip photoresist from the surfaces of semiconductorworkpieces. At step 200, the workpieces 20 that are to be stripped areplaced in, for example, a Teflon wafer cassette. This cassette is placedin a closed environment, such as in chamber 15. Chamber 15 and itscorresponding components may be constructed based on a well known spraysolvent system or spray acid such as those available from Semitool,Inc., of Kalispell, Mont., U.S.A. Alternatively, the semiconductorworkpieces 20 may be disposed in chamber 15 in a carrierless manner,with an automated processing system, such as described in U.S. Pat. No.5,784,797.

[0064] At step 205, heated deionized water is sprayed onto the surfacesof the semiconductor workpieces 20. The heated deionized water heats thesurfaces of the semiconductor workpieces 20 as well as the enclosedenvironment of the chamber 15. When the spray is discontinued, a thinliquid film remains on the workpiece surfaces. If the surface ishydrophobic, a surfactant may be added to the deionized water to assistin creating a thin liquid boundary layer on the workpiece surfaces. Thesurfactant may be used in connection with hydrophilic surfaces as well.Corrosion inhibitors may also be used with the aqueous ozone, thinboundary layer process.

[0065] The surface boundary layer of deionized water is controlled atstep 210 using one or more techniques. For example, the semiconductorworkpieces 20 may be rotated about axis 35 by rotor 30 to therebygenerate centripetal accelerations that thin the boundary layer. Theflow rate of the deionized water may also be used to control thethickness of the surface boundary layer. Lowering of the flow rateresults in decreased boundary layer thickness. Still further, the mannerin which the deionized water is injected into the chamber 15 may be usedto control the boundary layer thickness. Nozzles 40 may be designed toprovide the deionized water as micro-droplets thereby resulting in athin boundary layer.

[0066] At step 215, ozone is injected into the fluid flow path 60 duringthe water spray, or otherwise provided to the internal chamberenvironment of chamber 15. If the apparatus of FIG. 2 is utilized, theinjection of the ozone continues after the spray has shut off. If theworkpiece surface begins to dry, a brief spray is preferably activatedto replenish the liquid film on the workpiece surface. This ensures thatthe exposed workpiece surfaces remain wetted at all times and, further,ensures that the workpiece temperature is and remains elevated at thedesired reaction temperature. It has been found that a continuous sprayof deionized water having a flow rate that is sufficient to maintain theworkpiece surfaces at an elevated temperature, and high rotationalspeeds (i.e., >300 rpm, between 300 and 800 rpm, or even as high as orgreater than 1500 rpm) generates a very thin boundary layer whichminimizes the ozone diffusion barrier and thereby leads to an enhancedphotoresist stripping rate. As such, the control of the boundary layerthickness is used to regulate the diffusion of reactive ozone to thesurface of the wafer.

[0067] The surface layer thickness may range from a few molecular layers(e.g., about 1 micron), up to 100 microns, (typically 50-100 microns),or greater.

[0068] While ozone has a limited solubility in the heated deionizedwater, the ozone is able to diffuse through the water and react withphotoresist at the liquid/resist interface. It is believed that thepresence of the deionized water itself further assists in the reactionsby hydrolyzing the carbon-carbon bonds of organic deposits, such asphotoresist, on the surface of the wafer. The higher temperaturepromotes the reaction kinetics while the high concentration of ozone inthe gas phase promotes diffusion of ozone through the boundary layerfilm even though the high temperature of the boundary layer film doesnot actually have a high concentration of dissolved ozone.

[0069] Elevated or higher temperatures means temperatures above ambientor room temperature, that is temperatures above 20 or 25° and up toabout 200° C.

[0070] Preferred temperature ranges are 25-150°, more preferably 55-120°or 75-115° C., and still more preferably 85-105° C. In the methodsdescribed, temperatures of 90-100° C., and preferably centering around95° C. may be used.

[0071] After the semiconductor workpieces 20 have been processed throughthe reactions of the ozone and/or liquid with the materials to theremoved, the workpieces are subject to a rinse at 220 and are dried atstep 225. For example, the workpieces may be sprayed with a flow ofdeionized water during the rinse at step 220. They may then be subjectto any one or more known drying techniques thereafter at step 225.

[0072] In the described processes, elevated temperatures are used toaccelerate the reaction rates at the wafer surface. One manner in whichthe surface temperature of the wafer may be maximized is to maintain aconstant delivery of heated processing liquid, such as water or steam,during the process. The heated processing liquid contacts and heats thewafer during processing. However, such a constant delivery may result insignificant waste of the water or other processing liquid. In order toconserve water and achieve the thinnest possible boundary layer, a“pulsed flow” of liquid or steam may be used. In instances in which sucha “pulsed flow” fails to maintain the requisite elevated wafer surfacetemperatures, an alternative manner of maintaining the wafer surfacetemperature may be needed. One such alternative is the use of a “hotwall” reactor that maintains the wafer surface and processingenvironment temperatures at the desired level. To this end, the processchamber may be heated by, for example, one or more embedded heatedrecirculating coils, a heating blanket, irradiation from a thermalsource (e.g., and infrared lamp), etc.

[0073] In laboratory experiments, a 150 mm silicon wafer coated with 1micron of photoresist was stripped in accordance with the teachings ofthe foregoing process. The processing chamber was pre-heated by sprayingdeionized water that was heated to 95 degrees Celsius into theprocessing chamber for 10 minutes. During the cleaning process, a pulsedflow of deionized water heated to 95 degrees Celsius was used. Thepulsed flow included an “on time” of approximately five seconds followedby an “off time” of 10 seconds. The wafer was rotated at 800 rpm and thepulsed flow of deionized water was sprayed into the processing chamberthrough nine nozzles at a rate of 3 liters per minute. Ozone wasinjected into the processing chamber through a separate manifold at arate of 8 liters per minute at a concentration of 12 percent. Theresultant strip rate was 7234 Angstroms/min.

[0074] At a higher ozone flow rate, made possible by using a highcapacity ozone generator for injecting ozone into the processing chamberat a rate of 12 liters per minute and having a concentration of 19percent, the resultant strip rates can be further increased to in excessof 8800 Angstroms/minute.

[0075] There are many benefits resulting from the use of thesemiconductor cleaning processes described above. One of the mostsignificant benefits is that the conventional 4-chem clean process maybe reduced to a two-chemical step process while retaining the ability toremove organics, remove particulates, reduce metals and remove silicondioxide. Process times, chemical consumption, water consumption andwaste generation are all also significantly reduced. A further benefitof the foregoing process is its applicability to both FEOL and BEOLwafers and strip processes. Laboratory tests indicate that there is noattack on metals such as aluminum, titanium, tungsten, etc. A knownexception is copper, which forms a copper oxide in the presence ofozone. This oxide is not a “hard” and uniform passivation oxide, such asthe oxide that forms on metals like aluminum. As a result, the oxide canbe readily removed.

[0076] A still further benefit is the higher ozone flow rates andconcentrations can be used to produce higher strip rates under variousprocessing conditions including lower wafer rotational speeds andreduced temperatures. Use of lower temperatures (between 25 and 75° C.and preferably from 25-65° C. (rather than at e.g., 95° C. as describedabove) may be useful where higher temperatures are undesirable.

[0077] One example where this is beneficial is the use of the processwith BEOL wafers, wherein metal corrosion may occur if the metal filmsare exposed to high temperature de-ionized water. Correspondingly,processing at ambient temperatures may be preferred. The gain in striprates not realized, as a result of not using higher temperatures, isoffset by increases in strip rate due to the increased ozone flow ratesand concentrations. The use of higher ozone concentration can offset theloss of kinetic energy from using lower temperatures.

[0078] With reference again to FIG. 3, it will be recognized thatprocess steps 205-215 may be executed in a substantially concurrentmanner. Additionally, it will be recognized that process steps 205-215may be sequentially repeated using different processing liquids. In suchinstances, each of the processing liquids that are used may bespecifically tailored to remove a respective set of contaminants.Preferably, however, it is desirable to use as few different processingliquids as possible. By reducing the number of different processingliquids utilized, the overall cleaning process is simplified andreducing the number of different processing liquids utilized minimizeschemical consumption.

[0079] A single processing liquid may be used to remove organiccontaminants, metals, and particles in a single cycle of process steps205-215. The processing liquid is comprised of a solution of deionizedwater and one or more compounds, such as HF or HCl, so as to form anacidic processing liquid solution.

[0080] The use of a hydrofluoric acid solution in the process steps setforth at 205-215 provides numerous advantages, including the following:

[0081] 1. Removal of organic contaminants—The oxidation capability ofthe process has been demonstrated repeatedly on photoresist. Strip ratesoften exceed 8800A/minute. Considering the fact that in cleaningapplications, organic contamination is generally on the molecular level,the disclosed process has ample oxidation capacity.

[0082] 2. Removal of oxide and regeneration of a controlled chemicaloxide—Depending on the temperature of the solution and the concentrationof HF in solution, a specific etch rate may be defined. However, theozone will diffuse through the controlled boundary layer and regeneratethe oxide to prevent the wafer from becoming hydrophobic. A 500:1 H₂O:HFmixture at 65 degrees C. will etch SiO₂ at a rate of about 6A/minute.The same solution at 25 degrees C. will etch SiO₂ at about 2A/minute. Atypical “native” oxide is generally self limiting at a thickness of8-12A, which is generally the targeted thickness for the oxide removal.

[0083] 3. Removal of particles—Although the acidic solutions do not havethe favorable zeta potential present in the SC1 clean noted above,particle removal in the disclosed process with an HF processing liquidhas still been shown to be significant, as it uses the same removalmechanism of etching and regenerating the oxide surface.

[0084] 4. Removal of metals—In laboratory experiments, wafers wereintentionally contaminated with iron, nickel and copper. The disclosedprocess with an HF containing processing liquid showed a reduction inmetals of over three orders of magnitude. As an added enhancement, HClcan be used in place of the HF to accomplish the metals removal,although this does not have the same degree of oxide and particleremoval capability. The combination of HF and HCl is a further benefit,as each of these chemistries has significant metals removal capability,but the regeneration of the oxide surface in conjunction with theconversion of metals to metallic oxides and the symbiotic interaction ofthe two acid halides creates an exceptionally favorable environment formetal removal.

[0085] An oxide-free (hydrophobic) surface may be generated, if desired,by using a final HF step in an immersion cell or by use of an HF vaporstep after the metals removal.

[0086] With the use of HF and ozone, the boundary layer is preferablymaintained thick enough to achieve good etch uniformity, by selectingflow rates of liquid onto the workpiece surface, and removal rates ofliquid from the workpiece surface. The boundary layer of the liquid onthe workpiece surface is preferably maintained thick enough so that theetch uniformity is on the order of less than 5%, and preferably lessthan 3% or 2% (3-sigma divided by the mean).

[0087] In the HF and ozone process, the ozone concentration ispreferably about 3-35% or 10-20% by weight (in oxygen). The ozoneconcentration is largely dependent on the etch rate of the aqueous HFsolution used. When processing silicon, it is desirable that the siliconsurface not be allowed to go hydrophobic, indicating the completeetching of the passivating silicon dioxide surface. HF concentrationused is typically 0.001 to 10% or 0.01 to 1.0% (by weight). In general,the lower concentrations are preferred, with a concentration of about0.1% providing very good cleaning performance (with an etch rate of 8Aof thermal oxide per minute at 95 C.). The HF solution may includehydrochloric acid to enhance metal removal capability. If used, the HCltypically has a range of concentrations similar to the ranges describedabove for HF.

[0088] In the HF and ozone process, a temperature range from 0° C. up to100° C. may be used. Higher temperatures may be used if the process isconducted under pressure. Particle removal capability of this process isenhanced at elevated temperatures. At ambient temperature, the particleremoval efficiency of dried silicon dioxide slurry particles withstarting counts of around 60,000 particles larger than 0.15 microns, wasabout 95%. At 65° C., this efficiency increased to 99%. At 95° C., theefficiency increased to 99.7%. Although this may appear to be a slightimprovement, the difference in final particle count went from 3000 to300 to about 100 particles, which can be very significant in themanufacture of semiconductor devices.

[0089] The HF and ozone process may be included as part of a cleaningsequence, for example: 3:00 (minutes) of HF/O3>3:00 SC1>3:00 HF/O3. Inthis sequence, the cleaning efficiency increased to over 99.9%. Incontrast, the SC1 alone had a cleaning efficiency of only 50% or less.Similar results have been achieved when cleaning silicon nitrideparticles as well.

[0090] The steps and parameters described above for the ozone processesapply as well to the ozone with HF and ozone process. These processesmay be carried out on batches of workpieces in apparatus such asdescribed in U.S. Pat. No. 5,544,421, or on individual workpieces in anapparatus such as described in PCT/US99/05676.

[0091] Typical chemical application times are in the range of 1:00 to5:00. Compared to a 4-chem clean process time of around 20:00, thedisclosed process with an HF and/or HCl containing processing liquidbecomes very attractive. Typical H₂O:HF:HCl concentration ratios are onthe order of 500:1:1 to 50:1:1, with and without HF and/or HCl. Higherconcentrations are possible, but the economic benefits are diminished.It is important to note that gaseous HF or HCl could be injected intowater to create the desired cleaning chemistry as well. Due todifferences in processor configurations and desired cleaningrequirements, definition of specific cleaning process parameters willvary based on these differences and requirements.

[0092] The process benefits include the following:

[0093] 1. Reduction in the amount and types of chemicals used in thecleaning process.

[0094] 2. Reduction in water consumption by the elimination of thenumerous intermediate rinse steps required.

[0095] 3. Reduction in process time.

[0096] 4. Simplification of process hardware.

[0097] The disclosed processes are counter-intuitive. Efforts have beenmade for a number of years to replace hydrogen peroxide with ozone inchemistries such as SC1 and, to a lesser degree, SC2. These efforts havelargely failed because they have not controlled the boundary layer andhave not introduced the ozone in such a manner that diffusion throughthe boundary layer is the controlling mechanism instead of dissolutioninto the boundary layer. While the cleaning efficiency of conventionalsolutions is greatly enhanced by increasing temperature, it isrecognized that the solubility of ozone in a given liquid solution isinversely proportional to the temperature of the solution. Thesolubility of ozone in water at 1 degrees Celsius is approximately 100ppm. At 60 degrees Celsius, this solubility drops to less than 5 ppm. Atelevated temperatures, the ozone concentration is thus insufficient topassivate (oxidize) a silicon wafer surface quickly enough to ensurethat pitting of the silicon surface will not occur. Thus the twomechanisms are in conflict with one another when attempting to optimizeprocess performance.

[0098] Tests have demonstrated that by applying the boundary layercontrol techniques explained in connection with the presently disclosedprocesses, it is possible to process silicon wafers using a 4:1water:ammonium hydroxide solution at 95 C. and experience an increasesurface roughness (RMS) of less than 2 angstroms. When this samesolution is applied in an immersion system or in a conventional spraysystem, RMS surface roughness as measured by atomic force microscopyincreases by more than 20 angstroms and the maximum surface roughnessexceeds 190 angstroms. Additionally, while a conventional process willpit the surface to such a degree as to render the surface unreadable bya light-scattering particle counter, the boundary controlled techniquehas actually shown particle reductions of up to 50% on the wafersurface.

[0099] In the case of oxidizing and removing organic contamination,conventional aqueous ozone processes show a strip rate on photoresist (ahydrocarbon film) of around 200-700 angstroms per minute. In theboundary layer controlled system of the disclosed processes, the rate isaccelerated to 2500 to 8800. angstroms per minute in a spray controlledboundary layer, or higher when the boundary layer is generated andcontrolled using steam at 15 psi and 126 degrees C.

[0100] The disclosed processes are suitable for use in a wide range ofmicroelectronic fabrication applications. One issue which is of concernin the manufacture of semiconductor devices is reflective notching. Inorder to expose a pattern on a semiconductor wafer, the wafer is coatedwith a photo-active compound called photoresist. The resistance film isexposed to a light pattern, thereby “exposing” the regions to which thelight is conveyed. However, since topographic features may exist underthe photoresist, it is possible for the light to pass through thephotoresist and reflect off of a topographic feature. This results inresist exposure in an undesirable region. This phenomenon is known as“reflective notching.” As device density increases, reflective notchingbecomes more of a problem.

[0101] A similar issue arises as a result of the reflectance normal tothe incident angle of irradiation. Such reflectance can createdistortions in the exposure beam through the phenomenon of standing waveformation, thereby resulting in pattern distortion in the photoresist.

[0102] In order to combat these phenomena, the use of anti-reflectivecoating layers has become common. The photoresist films are typicallydeposited either on top of or below an anti-reflective coating layer.Since both the photoresist layer and the anti-reflective coating layerare merely “temporary” layers used in intermediate fabrication steps,they must be removed after such intermediate fabrication steps arecompleted.

[0103] It has been found that the process of FIG. 3 may be used with aprocessing liquid comprised of water and ammonium hydroxide to removeboth the photoresist and the anti-reflective coating in a singleprocessing step (e.g., the steps illustrated at 210-215). Although thishas been demonstrated at concentrations between 0.02% and 0.04% ammoniumhydroxide by weight in water, other concentrations are also consideredto be viable.

[0104] The process for concurrently removing photoresist and thecorresponding anti-reflective layer is not necessarily restricted toprocessing liquids that include ammonium hydroxide. Rather, theprincipal goal of the additive is to elevate the pH of the solution thatis sprayed onto the wafer surface. Preferably, the pH should be raisedso that it is between about 8.5 and 11. Although bases such as sodiumhydroxide and/or potassium hydroxide may be used for such removal, theyare deemed to be less desirable due to concerns over mobile ioncontamination. However, chemistries such as TMAH (tetra-methyl ammoniumhydroxide) are suitable and do not elicit the same a mobile ioncontamination concerns. Ionized water that is rich in hydroxyl radicalsmay also be used.

[0105] The dilute ammonium hydroxide solution may be applied in theprocess in any number of manners. For example, syringe pumps, or otherprecision chemical applicators, can be used to enable single-use of thesolution stream. In such an embodiment, it becomes possible to strip thephotoresist using a deionized water stream with ozone, and can concludethe strip with a brief period during which ammonium hydroxide isinjected into the aqueous stream. This assists in minimizing chemicalusage and waste generation. The application apparatus may also becapable of monitoring and controlling the pH the using the appropriatesensors and actuators, for example, by use of microprocessor control.

[0106] With reference to FIG. 4, there is shown yet a further embodimentof the ozone treatment system 227. In the embodiment of FIG. 4, one ormore nozzles 230 are disposed within the treatment chamber 15 to conductozone from ozone generator 75 directly into the reaction environment.The heated treatment fluid is provided to the chamber 15 through nozzles40 that receive the treatment fluid, such as heated deionized water,through a supply line that is separate from the ozone supply line. Assuch, injection of ozone in fluid path 60 is optional.

[0107] Another embodiment of an ozone treatment system is showngenerally at 250 in FIG. 5. In the system 250, a steam boiler 260 thatsupplies saturated steam under pressure to the process chamber 15 hasreplaced the pump mechanism. The reaction chamber 15 is preferablysealed to thereby form a pressurized atmosphere for the reactions. Forexample, saturated steam at 126 degrees Celsius could be generated bysteam boiler 260 and supplied to reaction chamber 15 to generate apressure of 35 psia therein during the workpiece processing. Ozone maybe directly injected into the chamber 15 as shown, and/or may beinjected into the path 60 for concurrent supply with the steam. Usingthe system architecture of this embodiment, it is thus possible toachieve semiconductor workpiece surface temperatures in excess of 100degrees Celsius, thereby further accelerating the reaction kinetics. Thesteam generator in FIG. 5 may be replaced with a heater(s) as shown inFIGS. 1-4. While FIGS. 4 and 5 show the fluid and ozone delivered viaseparate nozzles 40, they may also be delivered from the same nozzles,using appropriate valves.

[0108] A still further enhancement that may be made to any one of theforegoing systems is illustrated in FIG. 6. In this embodiment, anultra-violet or infrared lamp 300 is used to irradiate the surface ofthe semiconductor workpiece 20 during processing. Such irradiationfurther enhances the reaction kinetics. Although this irradiationtechnique is applicable to batch semiconductor workpiece processing, itis more easily and economically implemented in the illustrated singlewafer processing environment where the workpiece is more easilycompletely exposed to the UV radiation. Megasonic or ultrasonic nozzles40 may also be used.

[0109] With reference to FIG. 7, a further system 310 for implementingone or more of the foregoing processes is set forth. Of particular notein system 310 is the use of one or more liquid-gas contactors 315 thatare used to promote the dissolution of ozone into the aqueous stream.Such contactors are of particular benefit when the temperature of theprocessing liquid is, for example, at or near ambient. Such lowtemperatures may be required to control corrosion that may be promotedon films such as aluminum/silicon/copper.

[0110] The contactor 315 is preferably of a parallel counter-flow designin which liquid is introduced into one end and the ozone gas isintroduced into the opposite end. Such contactors are available frome.g., W. L. Gore Corporation, Newark, Del., USA. These contactorsoperate under pressure, typically from about 1 to 4 atmospheres (gauge).The undissolved gas exiting the contactor 315 may be optionally directedto the process chamber 320 to minimize gas losses. However, the ozonesupply 330 for the contactor 315 may or may not be the same as thesupply for direct delivery to the process chamber 320.

[0111] As described, the ozone gas may be separately sprayed, orotherwise introduced as a gas into the process chamber, where it candiffuse through the liquid boundary layer on the workpiece. The fluid ispreferably heated and sprayed or otherwise applied to the workpiece,without ozone injected into the fluid before the fluid is applied to theworkpiece.

[0112] Alternatively, the ozone may be injected into the fluid, and thenthe ozone containing fluid applied to the workpiece. In this embodiment,if the fluid is heated, the heating preferably is performed before theozone is injected into the fluid, to reduce the amount of ozonebreakdown in the fluid during the fluid heating. Typically, due to thelarger amounts of ozone desired to be injected into the fluid, and thelow solubility of the ozone gas in the heated fluid, the fluid willcontain some dissolved ozone, and may also contain ozone bubbles.

[0113] It is also possible to use aspects of both embodiments, that isto introduce ozone gas directly into the process chamber, and to alsointroduce ozone into the fluid before the fluid is delivered into theprocess chamber. Thus, various methods may be used for introducing ozoneinto the chamber.

[0114] The presently disclosed apparatus and methods may be used totreat workpieces beyond the semiconductor workpieces described above.For example, other workpieces, such as flat panel displays, hard diskmedia, CD glass, etc, may also have their surfaces treated using theforegoing apparatus and methods.

[0115] Although the preferred treatment liquid for the disclosedapplication is deionized water, other treatment liquids may also beused. For example, acidic and basic solutions may be used, depending onthe particular surface to be treated and the material that is to beremoved. Treatment liquids comprising sulfuric acid, hydrochloric acid,and ammonium hydroxide may be useful in various applications.

[0116] As described, one aspect of the process is the use of steam(water vapor at temperatures exceeding 100 C.) to enhance the strip rateof photoresist in the presence of an ozone environment. Preliminarytesting shows that a process using hot water at 95 C. produces aphotoresist strip rate of around 3000-4000 angstroms per minute.Performing a similar process using steam at 120-130 C. results in astrip rate of around 7000-8000 angstroms per minute. However, theresultant strip rate is not sustainable.

[0117] The high strip rate is achieved only when the steam condenses onthe wafer surface. The wafer temperature rapidly approaches thermalequilibrium with the steam, and as equilibrium is achieved, there is nolonger a thermal gradient to promote the formation of the condensatefilm. This results in the loss of the liquid boundary layer on the wafersurface. The boundary layer appears to be essential to promote theoxidation of the organic materials on the wafer surface. The absence ofthe liquid film results in a significant drop in the strip rate onphotoresist.

[0118] Additionally, once the steam ceases to condense on the wafersurface, the reaction environment experiences the elimination of anenergy source to drive the reaction kinetics. As steam condenses on thewafer surface, it must relinquish the heat of vaporization, which isapproximately 540 calories per gram. This energy then becomes availableto promote other reactions such as the oxidation of carbon compounds inthe presence of ozone or oxygen free radicals.

[0119] In view of these experimental observations, a method formaintaining the temperature of a surface such as a semiconductor wafersurface, is provided to ensure that condensation from a steamenvironment continues indefinitely, thereby enabling the use of steam inapplications such as photoresist strip in the presence of ozone. Thusthe formation of the liquid boundary layer is assured, as well as therelease of significant amounts of energy as the steam condenses.

[0120] To accomplish this, the wafer surface must be maintained at atemperature lower than that of the steam delivered to the processchamber. This may be achieved by attaching the wafer to atemperature-controlled surface or plate 350 which will act as a heatsink. This surface may then be temperature controlled either through theuse of cooling coils, a solid-state heat exchanger, or other means.

[0121] In a preferred embodiment, a temperature-controlled stream ofliquid is delivered to the back surface of a wafer, while steam andozone are delivered to an enclosed process region and the steam isallowed to condense on the wafer surface. The wafer may be rotated topromote uniform distribution of the boundary layer, as well as helpingto define the thickness of the boundary layer through centrifugal force.However, rotation is not an absolute requirement. The cooling streammust be at a temperature lower than the steam. If the cooling stream iswater, a temperature of 75 or 85-95 C. is preferably used, with steamtemperatures in excess of 100 C.

[0122] In another embodiment, and one which is relatively easy toimplement in a batch process, pulsed spray of cooling liquid is appliedperiodically to reduce the wafer temperature. Steam delivery may eitherbe continuous or pulsed as well.

[0123] The wafer may be in any orientation and additives such ashydrofluoric acid, ammonium hydroxide or some other chemical may beadded to the system to promote the cleaning of the surface or theremoval of specific classes of materials other than or in addition toorganic materials.

[0124] This process enables the use of temperatures greater than 100 C.to promote reaction kinetics in the water/ozone system for the purposeof removing organic or other materials from a surface. It helps ensurethe continuous formation of a condensate film by preventing the surfacefrom achieving thermal equilibrium with the steam. It also takesadvantage of the liberated heat of vaporization in order to promotereaction rates and potentially allow the removal of more difficultmaterials which may require more energy than can be readily delivered ina hot water process.

[0125] Thus, novel systems and methods have been described. Varioussubstitutions and modifications can of course be made without departingfrom the spirit and scope of the invention. The invention, therefore,should not be restricted, except to the following claims and theirequivalents.

1. A method for processing a workpiece to remove material from a firstsurface of the workpiece, comprising the steps of: providing steam ontothe first surface under conditions so that at least some of the steamcondenses and forms a liquid boundary layer on the first surface, withthe condensing steam contributing to maintaining the workpiece firstsurface at an elevated temperature; introducing gaseous ozone around theworkpiece under conditions where the ozone diffuses through the boundarylayer and reacts with the material on the first surface; and controllingthe temperature of the first surface to maintain condensation of thesteam.
 2. The method of claim 1 where the temperature of the firstsurface is controlled by cooling a second surface of the workpieceopposite to the first surface of the workpiece.
 3. The method of claim 2where the first surface is a front surface and the second surface is aback surface of the workpiece.
 4. The method of claim 2 where thetemperature of the first surface is controlled by contacting the secondsurface with a heat sink.
 5. The method of claim 4 where the heat sinkcomprises a plate of a solid state heat exchanger.
 6. The method ofclaim 4 where the heat sink is liquid cooled.
 7. The method of claim 2where the second surface is cooled by applying a temperature controlledflow of cooling liquid to the second surface.
 8. The method of claim 7where the cooling liquid is at a temperature lower than the temperatureof the steam.
 9. The method of claim 7 where the cooling liquid is attemperature of from about 75-95 degrees C.
 10. The method of claim 1further comprising the step of spinning the workpiece.
 11. The method ofclaim 1 where the steam is provided in pulses at timed intervals. 12.The method of claim 7 where the cooling liquid is provided in pulses attimed intervals.
 13. The method of claim 7 where the cooling liquid issprayed onto the second surface of the workpiece.
 14. The method ofclaim 1 further comprising the step of introducing an additive chemicalto the boundary layer.
 15. The method of claim 14 where the chemicalcomprises hydrofluoric acid, hydrochloric acid, or ammonium hydroxide.16. The method of claim 2 where the steam and ozone are provided ontothe first surface of the workpiece within an enclosed process regionwhile the second surface of the workpiece is cooled via a temperaturecontrolled stream of cooling liquid.
 17. The method of claim 1 furtherincluding the step of rotating the workpiece to assist in forming theliquid boundary layer.
 18. The method of claim 1 further including thestep of controlling the rate at which steam condenses onto the firstsurface of the workpiece to assist in forming the liquid boundary layer.19. The method of claim 1 where the steam contains a surfactant, toassist in forming the liquid boundary layer.
 20. The method of claim 1where the ozone reacts with the material, and causes removal of thematerial at a rate of at least 3000 angstroms per minute.
 21. The methodof claim 1 where the ozone reacts with the material and causes removalof the material at a rate of at least 7000 angstroms per minute.
 22. Themethod of claim 21 where the steam is provided at a temperature of atleast 120 degrees C.
 23. The method of claim 2 where the workpiece inthermal equilibrium with the heating of the first surface of theworkpiece by the condensing steam substantially equivalently offset bythe cooling of the second surface of the workpiece.
 24. A method fortreating a workpiece comprising the steps of applying steam onto thesurface of the workpiece and allowing at least some of the steam tocondense on is the surface; heating the surface of the workpiece, atleast in part with the condensing steam; forming a heated liquid layeron the surface of the workpiece at least in part with the condensedsteam; controlling the thickness of the heated liquid layer on thesurface of the workpiece; controlling the temperature of the heatedliquid layer on the surface of the workpiece to maintain thecondensation of steam; introducing ozone gas into the environment aroundthe workpiece with at least some of the ozone gas diffusing through theheated liquid layer to the surface of the workpiece, with the diffusedozone resulting in a chemical reaction at the surface of the workpieceexpedited by the heating of the workpiece.
 25. The method of claim 24where the steam condenses on surface of the workpiece.
 26. The method ofclaim 25 where the steam condenses on the heated liquid layer.
 27. Themethod of claim 24 where the workpiece is processed within a closedchamber and the ozone is supplied into the chamber as a dry gas.
 28. Themethod of claim 24 where the workpiece is processed within a sealedchamber under higher than ambient pressure.
 29. The method of claim 28where the steam has a temperature greater than 100 degrees C.
 30. Themethod of claim 24 where the heated liquid layer includes sulfuric acid,hydrochloric acid (HCL), hydrofluoric acid (HF), or a combination ofthem.
 31. The method of claim 24 where the layer of heated liquidincludes ammonium hydroxide.
 32. The method of claim 24 where the stepof controlling the thickness of the heated liquid layer includes atleast one of the steps of rotating the workpiece, adding a surfactant tothe heated liquid layer, and condensing the steam onto the surface ofthe workpiece at a controlled rate.
 33. The method of claim 24 where theozone is mixed with the steam.
 34. The method of claim 24 where thesteam is sprayed onto the workpiece.
 35. The method of claim 24 wherethe workpiece is processed for 1-5 minutes.
 36. The method of claim 24where the controlling the temperature step comprises cooling theworkpiece by placing the workpiece into contact with a cooling surface.37. The method of claim 24 where the controlling the temperature stepcomprises the step of applying a cooling liquid to the workpiece.
 38. Amethod for treating a workpiece, comprising the steps of: loading theworkpiece into a chamber; supplying steam into the chamber; heating theworkpiece, at least in part, with the steam; allowing at least somesteam to condense as a liquid on the workpiece, to form a layer ofheated liquid on the workpiece; controlling the temperature of theworkpiece to maintain condensation of the steam over a desired interval;introducing ozone gas into the chamber, with at least some of the ozonegas diffusing through the layer of heated liquid and chemically reactingwith the workpiece.